In the semiconductor industry the wafer size on which devices are fabricated has been steadily increasing, which has resulted in a dramatic decrease of cost per unit cell. The maximum size of wafers used in the fabrication of magnetic thin film heads has remained a steady size, between five and six inches in diameter, for many years. One of the key reasons for this is that it is necessary to provide a 1000 oersted (Oe) magnetic field at the center of the wafer during plating and also during annealing to overcome the demagnetizing field in the individual tiny devices and to achieve intrinsic magnetic anisotropy in the deposited magnetic films. The demagnetizing field greatly depends on the size, shape and thickness of the head features. Some assistance in overcoming the demagnetizing field is achieved by plating magnetic films through narrow photo resist frames providing pseudo continuous film but even that is not sufficient when the dimensions of the pattern become very small and at the same time it is necessary to make films relatively thick. The demagnetizing field at such edges, unless the films are laminated by a non-magnetic material, can reach the value of the saturation magnetization of the film and it becomes very difficult to achieve any degree of the intrinsic magnetic anisotropy in the deposited magnetic films.
Electroplating is typically performed in an electrolytic cell having an anode (positive electrode) and a cathode (negative electrode). The anode can have the same chemical composition as the material being plated, or it may contain only one element of the material being plated. The cathode is usually the object to be electroplated (usually a metal, ceramic, or polymer structure). The anode and cathode are enveloped in an electroplating solution or bath containing plating ions of the metals being plated. In the electroplating process, metallic plating cations fix on the cathode to form a thin layer of metal plating (such as chromium, copper, nickel, iron, silver, and/or cobalt) when an electric current is passed through the solution. The solution is generally a salt aqueous mixture.
Magnetic sensors and heads on disk drives and tape drives use magnetically anisotropic films formed by electroplating a magnetic alloy under the influence of an orienting magnetic field. The electroplated film exhibits magnetic anisotropy in the plane of the film, the direction of the orienting field applied during deposition becoming the longitudinal, preferred, or easy axis of magnetization in the plated coating; and the orthogonal direction becoming the transverse or hard axis of magnetization. It is desirable for the electrodeposited magnetic film to have a large high frequency magnetic permeability. Such magnetic films have a magnetic anisotropy; directional fields are typically used to switch the device from one direction to another.
The magnetic field used in electroplating is usually provided by a permanent magnet built around the plating tank so that the plating tank and the cathode holder with the wafer are sitting in the center of the horse shoe-shaped magnet. The cathode holder is generally stainless steel. To maximize the magnitude of the magnetic field the top surface of the wafer is placed at approximately the level of the pole tips of the magnet.
Using even the highest commercially available permanent magnets it has not been possible to achieve 1000 Oe in the middle of a plating tank capable of accommodating an 8-inch wafer. The magnetic field can be increased to 1000 Oe and beyond only by using an electromagnet. Electromagnetic use has its drawbacks. Electromagnets are much more costly than permanent magnets, much too big (they occupy ten to twenty times the volume of the permanent magnet), and they require such a high current and dissipate so much heat that it is necessary to water cool the magnet. This greatly increases the square foot area of the manufacturing plant. The electromagnets also require a much higher operating cost (cost of high current electricity and of the cooling water).
This is the key reason why the entire thin film magnetic head industry has used permanent magnets with a maximum wafer size of 6 inches. Electroplating is done in a magnetic field when plating magnetic films such as permalloy. An applied field in the plane of the plated film creates a uniform magnetic easy axis in the film. The magnet gap must be large enough to span the wafer and plating tank. This introduces a major limitation in the field strength and uniformity for magnets of reasonable cost with available hard magnet materials. For electromagnets, large coils are needed. Another drawback with permanent magnets is that the magnets are expensive and the magnetic field interferes with the insertion and removal of the anode, which is usually a magnetic material such Nickel or Cobalt.
Further processing of the magnetic films by heating the films in the presence of the in-plane field is used to further enhance the magnetic axis uniformity and magnetic permeability of the films. The drawback is that yet another magnet is needed for the annealing station. Existing systems use a magnet in a fixed location for each plating tank and an annealing station where the magnetic materials are entirely external to the plating tank.
There is a need for a method of fabricating magnetic storage heads to overcome the shortcomings of the prior art.